Actual non-player character followers are limited by charisma + Master Persuasion perk, but Dog doesn't count against that limit, as noted, and you can also have a Familiar that's pretty impressive at max magical aptitude, it's also a permanent follower that doesn't count against your total. Then you can have as many raised undead, dominated, or summoned as you can sustain with your magick or chemicals, and you can get as many mechs as you can build.
My two biggest parties were a non-combatant puppetmaster type and a mad tinker idiot savant. When you get up to 12 members things start getting laggy.
Not really. You won't get their voiced dialog, or most of their dialog, and the spell wears off if you sleep or fast travel. After the spell wears off they still hate you, so you'll have to kill or evade them, or otherwise get rid of them.
Out of all the followers in the game, there are like 6-7 who have voice acting. Virgil and Magnus are the ones you get the earliest. There are more as you progress through the story. What only matters is to get these voiced followers, not how many you have currently.
As for the number of followers you can have at any one point, it depends on your CHA. I've been playing too many games lately so I might get this mixed up, but I guess it's CHA/4?
i know people are going to get pretty sick of me asking, but is there a follower limit, from what i've read you can get a maximum of 20 points in charisma so that means 5 followers max plus having more persuasion can get me an extra follower, i'm excluding any summoned or made followers, i mean real characters in the game
and for voiced followers i take it in order to get Gar i have to get rid of either Virgil or Magnus